Analysis of incidence and mortality for malignant neoplasms of the digestive system among the liquidators in 1986-1997

The paper provides analysis of information about incidence and mortality with respect to malignant neoplasms of the digestive system in the Chernobyl liquidators accumulated in the Russian National Medical and Dosimetric Registry (RNMDR) in the period from 1986 to the beginning of 1998. The study includes male liquidators registered in six regional centers of the RNMDR providing most reliable medical and dosimetric data on an annual basis, namely Northwest, Volgo-Vyatsky, Central-Chernozemny, Povolzhsky, North-Caucasian and Urals. The number of liquidators under study is 96026 persons, which accounts for 57% of all liquidators registered in the RNMDR. The mean dose in the study cohort is 108 mGy, the mean age at the time of entry in the zone is 34.3 years and the total accumulated number of person-years is 1011727. The incidence and mortality rates for cancers of the digestive system were compared for liquidators and the population of Russia in general through calculation of the standardized incidence ratio (SIR) and the standardized mortality ratio (SMR). The values of SIR and SMR with 95% confidence intervals (CI) for malignant neoplasms of the digestive system were estimated to be 0.88 (0.80; 0.97) and 0.72 (0.64; 0.80), respectively. For liquidators who arrived in the zone in 1986 these are 0.97 (0.85; 1.11) and 0.81 (0.70; 0.94), respectively. During the period of 1991-1997, when SIR in liquidators became stable, the values of SIR and SMR with 95% CI for malignant neoplasms of the digestive system were 1.00 (0.90; 1.10) and 0.87 (0.78; 0.98), respectively. For liquidators who arrived in the zone in 1986 these values were 1.15 (1.00; 1.33) and 1.02 (0.86; 1.19), respectively. Estimation of radiation risks for this class of diseases did not reveal any statistically significant increase in cancer incidence or mortality with increase in external radiation dose in liquidators.